Check for power at a coil and fire it by hand

Steps

• Game on in attract mode, playfield raised; meter on DC volts (100 V range), black probe on the side rail.
• Each coil lug should read about 43 V; each of the three flipper coil lugs should too.
• To fire the coil, clip a lead to the side rail and briefly touch the lug with the unbanded end of the diode. Touching the banded (power) lug to ground will likely blow a fuse (page 22).
• No fire: damaged coil or no power. With power off, a good coil reads about 3 to 15 ohms.

This check is done with the game on; keep fingers off the line-voltage wiring and the high-voltage display circuit.

Systems

• Bally MPU AS-2518-17
• Bally MPU AS-2518-35

Related tips

• Check every coil's resistance before first power-up
• No playfield coils work
• Use the solenoid test to find a coil that does not fire
• No coils work at all
• Solenoids fire out of order in solenoid test
• The wrong coil fires (check the ROMs and the expander)
• Saucer fires at power-on and blows the playfield fuse: wrong coil killed its transistor
• Drop target coil won't fire in test: replace its diode

Source: Repairing Bally Electronic Pinball Games from 1977 to 1985, Part Three, Clay Harrell (pinrepair.com)